The semiconductor industry has experienced continuous rapid growth due to constant improvements in the integration density of various electronic components (i.e., transistors, diodes, resistors, capacitors, etc.). For the most part, this improvement in integration density has come from repeated reductions in minimum feature size, allowing more components to be integrated into a given chip area. These integration improvements are essentially two-dimensional (2D) in nature, in that the volume occupied by the integrated components is essentially on the surface of the semiconductor wafer. Although dramatic improvements in lithography have resulted in considerable improvements in 2D integrated circuit formation, there are physical limitations to the density that can be achieved in two dimensions. One of these limitations is the minimum size needed to make these components. Also, when more devices are put into one chip, more complex designs are required. An additional limitation comes from the significant increase in the number and length of interconnections between devices as the number of devices increases. When the number and the length of interconnections increase, both circuit RC delay and power consumption increase. Among the efforts for resolving the above-discussed limitations, three-dimensional integrated circuit (3DIC) and stacked dies are commonly used.
Through-silicon vias (TSVs) are thus used in 3DIC and stacked dies for connecting dies. In this case, TSVs are often used to connect the integrated circuits on a die to the backside of the die. In addition, TSVs are also used to provide short grounding paths for grounding the integrated circuits through the backside of the die, which may be covered by a grounded metallic film. An integrated circuit generally includes contact regions for connecting the integrated circuit to other circuits. Contact-bonding (CB) pads are generally formed in metal layers, e.g., the top level of metal, which connect to the TSV through a post passivation interconnect (PPI) structure. A conventional PPI process, however, provides weak adhesion to the CB pad and causes a high contact resistance. Accordingly, there is a need for an improved structure and a method of fabricating such to avoid the shortcomings of the conventional process.